Catalytic converters and lambda probes are used in the exhaust gas system of internal combustion engines for optimizing the pollutant emissions and for the exhaust gas aftertreatment. The lambda probes ascertain the oxygen content of the exhaust gas, which is used for regulating the air-fuel mixture supplied to the internal combustion engine and thus for regulating the exhaust gas lambda upstream from a catalytic converter. Via a lambda closed loop control, the air and fuel supply of the internal combustion engine is regulated in such a way that an optimal composition of the exhaust gas is achieved for the exhaust gas aftertreatment by the catalytic converters provided into the exhaust tract of the internal combustion engine. In the case of Otto engines, a lambda of 1, i.e., a stoichiometric air to fuel ratio, is regulated as a rule. However, catalytic converters achieve their purification effect only when heated to a sufficiently high temperature. In Otto engines for low-emission concepts a main share of the emissions is produced in the cold-start phase. As a result, very rapid heating of the catalytic converters following the engine start is required in order to convert the raw emissions as completely and quickly as possible. Moreover, the raw emissions themselves must be as low as possible in the cold start.
To heat the catalytic converters, the internal combustion engine can be operated using a rich mixture and secondary air may be metered in the exhaust gas tract between the outlet valves of the internal combustion engine and the catalytic converter in addition. Hydrocarbons in the exhaust gas are then combusted with the oxygen of the secondary air upstream from or inside the catalytic converter and heat it up. In an alternative heating method, the internal combustion engine may be operated at a reduced efficiency, so that the exhaust gas assumes a relatively high temperature and heats up the catalytic converter. To reduce the efficiency, it is common practice to increase the air quantity in the combustion chambers, to adjust the ignition angle in the retarded direction and to thereby generate a torque reserve. This causes less combustion energy to be converted into kinetic energy and the exhaust gas is expelled from the combustion chamber at a higher temperature. However, depending on the combustion method, this often has the result that a greater quantity of nitrogen oxide is contained in the exhaust gas as the exhaust gas temperature rises or an exhaust gas heat flow increases. In the case of lowest emission concepts, however, stringent limit values for the discharge of hydrocarbons and nitrogen oxides must be observed, so that the reduction of the pollutant emissions in the exhaust gas within the start/catalytic converter heating phase is of the greatest importance.